Gas spring piston, gas spring assembly and method

ABSTRACT

A gas spring piston includes a piston body with an end wall and a side wall that projects longitudinally from the end wall. The side wall includes an outer surface and a retainment ridge spaced longitudinally from the end wall such that the outer surface is disposed between the retainment ridge and the end wall. The retainment ridge projects radially-outwardly beyond the outer surface such that a shoulder surface is formed adjacent the outer surface. The outer surface includes an engagement feature that is dimensioned to compressively engage an associated flexible wall. The engagement feature is positioned along the outer surface in spaced relation to the end wall and the shoulder surface of the retainment ridge. A gas spring assembly and a method of assembling a gas spring that include such a gas spring piston are also disclosed.

BACKGROUND

The subject matter of the present disclosure broadly relates to the artof spring devices and, more particularly, to a gas spring piston thatincludes a feature for locating a mounting bead of an associatedflexible wall along the gas spring piston. The subject matter of thepresent disclosure also relates to a gas spring assembly and a method ofassembling a gas spring that include such a gas spring piston.

The subject matter of the present disclosure may find particularapplication and use in conjunction with suspension systems of wheeledvehicles, and may be described herein with particular reference thereto.However, it is to be appreciated that the subject matter of the presentdisclosure is also amenable to use in other applications andenvironments, and that the specific uses shown and described herein aremerely exemplary. For example, the subject matter of the presentdisclosure could be used in support structures, height adjusting systemsand actuators associated with industrial machinery, components thereofand/or other such equipment.

Wheeled motor vehicles of most types and kinds include a sprung mass,such as a body or chassis, for example, and an unsprung mass, such as anaxle or other wheel-engaging member, for example, with a suspensionsystem disposed therebetween. Typically, a suspension system willinclude a plurality of spring devices as well as a plurality of dampingdevices that together permit the sprung and unsprung masses of thevehicle to move in a somewhat controlled manner relative to one another.Movement of the sprung and unsprung masses toward one another isnormally referred to in the art as jounce motion while movement of thesprung and unsprung masses away from one another is commonly referred toin the art as rebound motion.

In many applications and uses associated with wheeled motor vehicles,the suspension system of the vehicle is adapted and arranged such thatthere are substantially no operating conditions, during normal usage,under which the plurality of spring devices would be tensioned orotherwise undergo a tension load. That is, the configuration and/or useof conventional suspension systems is such that the spring devices arenot tensioned under during rebound motion and are generally used incompression under normal operating conditions. In such operatingenvironments, it is possible to utilize a gas spring assembly that has asimplified construction and minimal retention of the flexible wall onthe piston of the gas spring assembly in the direction opposite thatassociated with normal use.

As a more-specific example, a construction can be used in which an openend of the flexible wall thereof is “snapped-on” or otherwise press-fitonto the piston of the gas spring assembly. It will be appreciated thatsuch “snap-on” constructions can result in lower cost gas springassemblies, such as, for example, because a reduced number of componentscould be used and/or because simplified assembly and other manufacturingtechniques could be employed.

This “snap-on” interengagement between the open end of the flexible walland a portion of the piston normally provides sufficient retention forhandling and installation purposes. However, such constructions areoften deemed to be poorly suited for applications in which the gasspring assembly could be stretched or otherwise placed in tension, asthis could generate an undesirable separation between the flexible walland the piston of the gas spring assembly.

As such, it is believed desirable to develop a gas spring piston, aswell as a gas spring assembly and method of assembly including the same,that are capable of providing improved engagement of the flexible wallwith the gas spring piston, such as, for example, may be useful forproviding improved sealing between the flexible wall and the gas springpiston, providing improved retention of the flexible wall on the gasspring piston (e.g., during use of the gas spring assembly under tensionconditions), and/or overcoming other disadvantages of knownconstructions while maintaining a relatively low cost of manufacture andease of assembly.

BRIEF DESCRIPTION

One example of a gas spring piston in accordance with the subject matterof the present disclosure that is dimensioned to receive an open end ofan associated flexible wall can include a piston body having alongitudinal axis. The piston body can include a first piston end and asecond piston end spaced longitudinally from the first piston end. Afirst side wall can extend circumferentially about the axis andlongitudinally between the first and second piston ends. An end wall canextend transverse to the axis and interconnect with the first side wall.A second side wall can extend circumferentially about the axis andproject longitudinally from the end wall in a direction opposite thefirst side wall. The second side wall can include an outer surface and aretainment ridge disposed in longitudinally-spaced relation to the endwall such that the outer surface is disposed between the retainmentridge and the end wall. The retainment ridge can projectradially-outwardly beyond the outer surface such that a shoulder surfaceis formed adjacent the outer surface and extends radially-outwardlyalong the retainment ridge in approximate alignment with the end wall.The outer surface can include an engagement feature dimensioned tocompressively engage the associated flexible wall. The engagementfeature can be positioned along the outer surface inlongitudinally-spaced relation to the end wall and the shoulder surfaceof the retainment ridge.

One example of a gas spring assembly in accordance with the subjectmatter of the present disclosure can include a flexible wall having alongitudinal axis and extending circumferentially about the axis andlongitudinally between opposing first and second open ends such that theflexible wall at least partially defines a spring chamber. A first endmember can be operatively connected across the first open end of theflexible wall such that a substantially fluid-tight seal is formedtherewith. A gas spring piston can include an end wall extendingtransverse to the longitudinal axis, a first side wall extendinglongitudinally from the end wall in a first direction, and a second sidewall extending longitudinally from the end wall in a second directionopposite the first direction. The second side wall can include aretainment ridge disposed in longitudinally-spaced relation to the endwall such that an outer surface of the second side wall is disposedtherebetween. The retainment ridge can project radially-outwardly beyondthe outer surface such that a shoulder surface is formed along theretainment ridge that is disposed in facing relation to the end wall.The outer surface can include a first surface portion disposed adjacentthe end wall, a second surface portion disposed adjacent the shouldersurface and in longitudinally-spaced relation to the first surfaceportion, and a third surface portion disposed between the first andsecond surface portions. The third surface portion can at leastpartially define an engagement feature along the outer surface of thesecond side wall such that the engagement feature is positioned alongthe outer surface in longitudinally-spaced relation to the end wall andthe shoulder surface of the retainment ridge. The second open end of theflexible wall can be received along the second side wall between theretainment ridge and the end wall such that the flexible wallcompressively engages at least the engagement feature of the second sidewall.

One example of a method of assembling a gas spring in accordance withthe subject matter of the present disclosure can include providing aflexible wall that includes an open end and an end surface adjacent theopen end. The method can also include providing a piston having alongitudinal axis. The piston can include an end wall disposedtransverse to the axis, a first side wall that extends approximatelylongitudinally from the end wall in a first direction, and a second sidewall that extends approximately longitudinally from the end wall in asecond direction opposite the first direction. The second side wall caninclude a retainment ridge that extends circumferentially around thesecond side wall. The retainment ridge can include a shoulder surfacefacing the end wall. The second side wall can include an outer surfacehaving a first surface portion disposed adjacent the end wall, a secondsurface portion disposed adjacent the shoulder surface and inlongitudinally-spaced relation to the first surface, and a third surfaceportion disposed between the first and second surface portions. At leastone of the first and second surface portions can define an outermostcross-sectional dimension of the outer surface. The third surfaceportion can at least partially define an engagement feature along thesecond side wall that is positioned between the first and second surfaceportions and in spaced relation to the end wall and the shoulder surfaceof the retainment ridge. The method can further include positioning theopen end of the flexible wall adjacent the retainment ridge, and urgingthe open end of the flexible wall in an axial direction toward the endwall such that the open end is forced over the retainment ridge. Themethod can also include positioning the open end of the flexible wallalong the second side wall such that such that the end surface of theflexible wall compressively engages at least the engagement feature ofthe second side wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, in partial cross section, of one example of a gasspring assembly that includes a gas spring piston in accordance with thesubject matter of the present disclosure.

FIG. 2 is an enlarged cross-sectional view of the portion of theflexible wall and gas spring piston identified in Detail 2 of FIG. 1.

FIG. 3 is an exploded cross-sectional view of the portion of theflexible wall and gas spring piston in FIG. 2 prior to assembly.

DETAILED DESCRIPTION

Turning, now, to the drawings wherein the showings are for the purposeof illustrating examples of the subject matter of the present disclosureand which are not intended as a limitation of the same, FIG. 1illustrates one example of a gas spring assembly 100 disposed betweenopposing structural components, such as upper and lower structuralcomponents USC and LSC of an associated vehicle (not shown), forexample. Gas spring assembly 100 is shown as having a longitudinal axisAX and includes a first end member, such as a top or bead plate 102, forexample, that is adapted for securement on or along one of thestructural components (e.g., upper structural component USC). It will beappreciated that the first end member can be secured along thestructural component in any suitable manner, such as, for example, byusing one or more threaded mounting studs 104 that extend throughcorresponding mounting holes HLS in one of the associated structuralcomponents (e.g., upper structural component USC).

Gas spring assembly 100 also includes an opposing second end member,such as a piston 106, for example, that is longitudinally spaced fromthe first end member and is adapted for securement on or along adifferent one of the structural components, such as lower structuralcomponent LSC, for example. Again, it will be appreciated that thesecond end member can be operatively connected to or otherwise securedon or along the structural component in any suitable manner, such as byusing one or more threaded fasteners 108 to extend through mountingholes HLS in the associated structural component (e.g., lower structuralcomponent LSC) and threadably engage a corresponding mounting feature inthe second end member, such as a threaded passage 110, for example.

Gas spring assembly 100 also includes a flexible sleeve or bellows 112that is operatively connected between the first and second end membersand at least partially defines a spring chamber 114 therebetween. In theexemplary arrangement shown in FIG. 1, flexible sleeve 112 includes aflexible wall 116 that extends between opposing first and second openends 118 and 120. Flexible wall 116 includes an inside surface 122 thatis in fluid communication with spring chamber 114 and an outside surface124 that abuttingly engages piston 106. As can be better seen in FIGS. 2and 3, flexible wall 116 also includes an end surface 126 that extendsbetween and connects the inside and outside surfaces along second openend 120. It will be appreciated that flexible wall 116 can be formed inany suitable manner, such as, for example, by using one or morefabric-reinforced, elastomeric plies or layers (not shown) and one ormore un-reinforced, elastomeric plies or layers (not shown). Optionally,an annular reinforcement member 128, such as a bead wire, for example,can be embedded within the flexible wall along second open end 120.

Returning to FIG. 1, first open end 118 can be secured on or along firstend member 102 in any manner suitable for forming a substantiallyfluid-tight seal therewith. For example, flexible sleeve 112 can includea mounting bead 130 formed along first open end 118 that can,optionally, include an annular reinforcement member 132, such as a beadwire, for example, embedded therein with first end member 102 securedalong or across the first open end of the flexible sleeve by capturingat least a portion of the mounting bead using a crimped edge connection134.

Piston 106 extends longitudinally between a first or upper end 136 and asecond or lower end 138. First end 136 is adapted to receive and form asubstantially fluid-tight seal with second open end 120 of flexiblesleeve 112. Second end 138 of piston 106 is adapted to abuttingly engagean associated structural component, such as lower structural componentLSC, for example. Additionally, as discussed above, piston 106 can besecured on or along the associated structural component in any suitablemanner, such as by using threaded fastener 108 and threaded passage 110,for example.

Piston 106 includes a piston body 140 and can also, optionally, includeone or more additional components and/or elements, such as one or morethreaded inserts (not shown), for example. The piston body has a firstor outer side wall 142 that extends generally longitudinally betweenfirst and second ends 136 and 138. In use, flexible wall 116 of flexiblesleeve 112 forms a rolling-lobe 144 that is displaced along first sidewall 142 as the gas spring assembly undergoes changes in overall height,such as, for example, may be due to variations in load conditionsapplied thereto, as is well understood by those of skill in the art. Itwill be recognized that a wide variety of shapes, profiles and/orconfigurations can and have been used in forming the first or outer sidewall of the piston assembly. As such, it will be appreciated that theprofile of first side wall 142 is merely exemplary in that the sameincludes a first portion 146 having an approximately frustoconical ortapered shape, a second wall portion 148 having a curvilinear shape, anda third portion 150 having an approximately cylindrical shape.

Piston body 140 also includes a first or upper end wall 152 that extendscircumferentially around axis AX and in an orientation that is generallytransverse to first side wall 142. Additionally, first end wall 152 isshown in FIGS. 1-3 as including an approximately planar portion 154 thattransitions into first side wall 142 at a curved or shoulder portion156. It will be understood, however, that first end wall 152 can takeany suitable shape, form and/or configuration. For example, shoulderportion 156 could have a larger or smaller radius and/or approximatelyplanar portion 154 could be at least partially curved or otherwisecontoured. Furthermore, the description of first end wall 152 asextending generally transverse to first side wall 142 is to be broadlyinterpreted. As one example, first end wall 152 could be approximatelyperpendicular to first side wall 142, such as is shown in FIGS. 1-3, forexample. Recognizing, however, that the first side wall and first endwall can take a wide variety of shapes, contours, forms and/orconfigurations, a wide range of relative angular orientations should beinterpreted as being generally transverse, such as a range of plus (+)or minus (−) 45 degrees from horizontal, for example.

As shown in FIGS. 1-3, piston body 140 further includes a second orinner side wall 158 that extends circumferentially around axis AX and inan orientation that is generally transverse, as previously defined, tofirst end wall 152. Second side wall 158 can take any suitable shape,form and/or configuration. As are more clearly illustrated in FIGS. 2and 3, the second side wall can, for example, include approximatelycylindrical inner and outer surfaces 160 and 162, and can have alongitudinal length dimension and extend in circumferentiallycontinuously and substantially uniformly around axis AX at approximatelythe same longitudinal length dimension. Additionally, second side wall158 can project from first end wall 152 in a direction generallyopposite second end 136 of piston body 140 and terminate at a second endwall 164, which is shown as being approximately planar. However, it willbe recognized that any alternate shape, form and/or configuration couldbe used.

Piston body 140 can also include a retainment ridge 166 that extendcircumferentially around axis AX and project radially-outwardly fromsecond side wall 158. In the exemplary embodiment shown in FIGS. 1-3,retainment ridge 166 includes an outermost edge 168 and a shouldersurface 170 that extends circumferentially around axis AX and radiallyoutwardly from outer surface 162 of second side wall 158 to outermostedge 168. Additionally, shoulder surface 170 is disposed in facingrelation to first end wall 152 and extends radially outwardly ingenerally transverse relation, as previously defined, to second sidewall 158. Retainment ridge 166 also includes an outer surface 172 thatextends generally circumferentially around axis AX and is oriented in adirection facing radially-outwardly and generally away from first endwall 152.

The second side wall of a gas spring piston in accordance with thesubject matter of the present disclosure also includes one or moreengagement features formed along an outer surface thereof and adapted tooperatively interengage a portion of the flexible sleeve or bellows.Such one or more engagement features can be substantially continuous(e.g., annular) or include two or more segments disposed incircumferentially spaced relation to one another along the second sidewall. Additionally, such one or more engagement features can extend intothe second side wall (e.g., concave), project out of the second sidewall (e.g., convex), or any combination thereof. Furthermore, such oneor more engagement features can be of any suitable size, shape, form orconfiguration (e.g., approximately U-shaped or approximately V-shaped).

In the exemplary arrangement in FIGS. 1-3, outer surface 162 of secondside wall 158 is shown as including a plurality of surface portions thatare arranged in longitudinal relation with respect to one another. Asurface portion 174 is disposed toward first end wall 152 and a surfaceportion 176 is disposed in longitudinally-spaced relation to surfaceportion 174 in a direction toward shoulder surface 170 such that asurface portion 178 is disposed therebetween. Surface portions 174 and176 are shown as being approximately cylindrical in shape and extendingcontinuously about the periphery of second side wall 158. Surfaceportion 178 is shown as including a curvilinear cross-sectional shapethat at least partially defines a groove 180 that operates as anengagement feature in accordance with the subject matter of the presentdisclosure. It will be appreciated, however, that another shape and/orconfiguration for surface portion 178 could alternately be used, asdiscussed above. For example, surface portion 178′, which is representedas a dashed line in FIG. 3, could project radially-outwardly fromsurface portions 174 and 176 and form a rib 180′ (FIG. 3) extending atleast partially about the periphery of the second side wall.Alternately, a plurality of rib portions (not shown) could be spacedapart from one another about the periphery of the second side wall.

As shown in FIG. 3, outer surface 162 includes an outermostcross-sectional dimension D1, such as, for example, may be establishedby one or more of surface portions 174 and 176. Surface portion 178extends radially-inwardly into second side wall 158 from along surfaceportions 174 and 176, and, thus, defines an engagement feature having aninnermost cross-sectional dimension D2 that is less than outermostcross-sectional dimension D1. Additionally, it will be recognized thatsurface portion 178 is disposed longitudinally along outer surface 162in spaced relation to both first end wall 152 and shoulder surface 170of retainment ridge 166 such that at least some of surface portion 174and surface portion 176 is disposed between surface portion 178 and thefirst end wall and the shoulder surface, respectively.

Second open end 120 is adapted to be received along outer surface 162 ofsecond side wall 158. In a preferred embodiment, end surface 126 willhave a cross-sectional dimension D3 that is less than at leastcross-sectional dimension D1 of second side wall 152. In such case,second open end 120 of flexible wall 116 can be forced over or otherwiseassembled over retainment ridge 166 and onto second side wall 158, as isrepresented by arrow AR1 in FIG. 3, such that end surface 126compressively engages at least surface portions 174 and 176 of outersurface 162. It is anticipated that at least a portion of the materialforming second open end 120 of flexible wall 116, such as the materialadjacent end surface 126, for example, will flow or otherwise bedeformed into compressive engagement with surface portion 178 that atleast partially forms groove 180. In particular, at least a portion ofthe material forming the second open end of the flexible wall would beexpected to compressively engage surface portion 178 in conditions inwhich reinforcement member 128 is disposed in approximate longitudinalalignment with groove 180, such as is shown in FIG. 3 by centerpointsCP1 and CP2. In such an arrangement, end surface 126 would be expectedto adopt a cross-sectional profile having approximately thecross-sectional profile of outer surface 162, such as is represented inFIG. 3 by dashed line 126′, for example.

The flow or other deformation of the material of the flexible walladjacent end surface 126 of second open end 120 into compressiveengagement with surface portion 178 of outer surface 162 can be achievedin any suitable manner, such as by making the opening that is at leastpartially defined by end surface 126 that extends through second openend 120 somewhat smaller in size than that of outer surface 162 ofsecond side wall 158. In such case, the relative difference in sizes cangenerate a compressive or interference fit between the two componentsresulting in material displacement into groove 180.

Additionally, it is well understood that reinforcement members, such asreinforcement members 128 and 130 are substantially inelastic incomparison with the material from which flexible wall 116 is at leastpartially formed. For example, reinforcement members 128 and 130 can beformed from an endless ring of wound metallic wire (e.g., steel) orsolid metallic wire (e.g., steel). Whereas, the elastomeric materialfrom which flexible wall 116 is at least partially formed can includeone or more plies, layers or other masses of synthetic rubber, naturalrubber and/or thermoplastic elastomer. Due, at least in part, to thecomparative differences in elasticity of the reinforcement member andthe elastomeric material of the flexible wall, material adjacentreinforcement member 128 would be expected to compressively engagesurface portion 178 of outer surface 162 under conditions in whichreinforcement member 128 is at least approximately aligned with groove180.

Piston body 140 can be formed from any suitable material or combinationof materials for providing the desired strength and retention propertiesof piston 106. Examples of materials that may be suitable for use informing the piston body can include fiber-reinforced thermoplastics,such as glass (or other) fiber-reinforced polypropylene and glass (orother) fiber-reinforced polyamide, for example, and high-strength(unfilled) thermoplastics, such as polyester, polyethylene and polyetheror any combination thereof, for example.

As used herein with reference to certain elements, components and/orstructures, numerical ordinals (e.g., “first end” and “second end”)merely denote different singles of a plurality and do not imply anyorder or sequence unless specifically defined by the claim language.Furthermore, the term “gas” is used herein to broadly refer to anygaseous or vaporous fluid. Most commonly, air is used as the workingmedium of gas spring devices, such as those described herein, as well assuspension systems and other components thereof. However, it will beunderstood that any suitable gaseous fluid could alternately be used.

While the subject novel concept has been described with reference to theforegoing embodiments and considerable emphasis has been placed hereinon the structures and structural interrelationships between thecomponent parts of the embodiments disclosed, it will be appreciatedthat other embodiments can be made and that many changes can be made inthe embodiments illustrated and described without departing from theprinciples of the subject novel concept. Obviously, modifications andalterations will occur to others upon reading and understanding thepreceding detailed description. Accordingly, it is to be distinctlyunderstood that the foregoing descriptive matter is to be interpretedmerely as illustrative of the present novel concept and not as alimitation. As such, it is intended that the subject novel concept beconstrued as including all such modifications and alterations insofar asthey come within the scope of the appended claims and any equivalentsthereof.

The invention claimed is:
 1. A gas spring piston dimensioned to receivean open end of an associated flexible wall, said gas spring pistoncomprising: a piston body having a longitudinal axis and including: afirst piston end; a second piston end spaced longitudinally from saidfirst piston end; a first side wall extending circumferentially aboutsaid axis and longitudinally between said first and second piston ends;an end wall extending transverse to said axis and interconnecting withsaid first side wall; and, a second side wall extendingcircumferentially about said axis and projecting longitudinally fromsaid end wall in a direction opposite said first side wall, said secondside wall including an outer surface and a retainment ridge disposed inlongitudinally-spaced relation to said end wall such that said outersurface is disposed between said retainment ridge and said end wall,said retainment ridge projecting radially-outwardly beyond said outersurface such that a shoulder surface is formed adjacent said outersurface and extends radially-outwardly along said retainment ridge inapproximate alignment with said end wall, said outer surface includingan engagement feature dimensioned to compressively engage an end surfaceof the associated flexible wall, said engagement feature beingpositioned along said outer surface in longitudinally-spaced relation tosaid end wall and said shoulder surface of said retainment ridge,wherein said engagement feature includes a groove extendingradially-inwardly into said second side wall, said outer surfaceincludes a first surface portion disposed between said end wall and saidengagement feature, a second surface portion disposed between saidshoulder surface and said engagement feature, and a third surfaceportion disposed between said first and second surface portions withsaid third surface portion at least partially defining said groove ofsaid engagement feature, and wherein said third portion includes acurvilinear cross-sectional profile extending into said second side wallin a concave orientation and at least partially forms said groove ofsaid engagement feature, and wherein said first and second surfaceportions have a linear cross-sectional profile and extend respectivelybetween said end wall and said engagement feature and said shoulder andsaid engagement feature, said first, second and third surface portionsdefining the entirety of said outer surface between said shouldersurface and said end wall.
 2. A gas spring piston according to claim 1,wherein said outer surface includes a first surface portion disposedbetween said end wall and said engagement feature and a second surfaceportion disposed between said shoulder surface and said engagementfeature such that said engagement feature is disposed inlongitudinally-spaced relation to said end wall and said shouldersurface.
 3. A gas spring piston according to claim 2, wherein at leastone of said first and second surface portions defines an outermostperipheral extent of said outer surface.
 4. A gas spring pistonaccording to claim 2, wherein at least one of said first and secondsurface portions has a substantially cylindrical outer peripheral shape.5. A gas spring piston according to claim 4, wherein each of said firstand second surface portions has a substantially cylindrical outerperipheral shape.
 6. A gas spring piston according to claim 1, whereinsaid engagement feature includes a groove extending radially-inwardlyinto said second side wall.
 7. A gas spring piston according to claim 6,wherein said groove extends substantially-continuously around said axisalong said outer surface of said second side wall.
 8. A gas springassembly comprising: a flexible wall having a longitudinal axis andextending circumferentially about said axis and longitudinally betweenopposing first and second open ends such that said flexible wall atleast partially defines a spring chamber, said flexible wall includingan inside surface, an outside surface, and an end surface extendingbetween and connecting said inside surface and said outside surface; afirst end member operatively connected across said first open end ofsaid flexible wall such that a substantially fluid-tight seal is formedtherewith; and, a gas spring piston including an end wall extendingtransverse to said longitudinal axis, a first side wall extendinglongitudinally from said end wall in a first direction, and a secondside wall extending longitudinally from said end wall in a seconddirection opposite said first direction; said second side wall includinga retainment ridge disposed in longitudinally-spaced relation to saidend wall such that an outer surface of said second side wall is disposedtherebetween, said retainment ridge projecting radially-outwardly beyondsaid outer surface such that a shoulder surface is formed along saidretainment ridge that is disposed in facing relation to said end wall,said outer surface including a first surface portion disposed adjacentsaid end wall, a second surface portion disposed adjacent said shouldersurface and in longitudinally-spaced relation to said first surfaceportion, and a third surface portion disposed between said first andsecond surface portions, said third surface portion at least partiallydefining an engagement feature along said outer surface of said secondside wall such that said engagement feature is positioned along saidouter surface in longitudinally-spaced relation to said end wall andsaid shoulder surface of said retainment ridge, said first, second andthird surface portions defining the entirety of said outer surfacebetween said shoulder surface and said end wall; said second open end ofsaid flexible wall received along said second side wall between saidretainment ridge and said end wall such that said end surface of saidflexible wall compressively engages at least said engagement feature ofsaid second side wall and said outside surface of said flexible wallengages said end wall.
 9. A gas spring assembly according to claim 8,wherein said flexible wall includes a reinforcement member at leastpartially embedded therein adjacent said second open end, and saidsecond open end being positioned along said outer surface of said secondside wall such that said reinforcement member is at least approximatelyaligned with said engagement feature.
 10. A gas spring assemblyaccording to claim 9, wherein said third surface portion has a concavecross-sectional shape extending radially-inwardly into said second sidewall such that said engagement feature includes a groove extending atleast partially around said outer surface.
 11. A gas spring assemblyaccording to claim 10, wherein said groove is an endless annular groovethat extends circumferentially about said axis along said outer surface.12. A gas spring assembly according to claim 10, wherein said thirdsurface portion has a cross-sectional centerpoint, said reinforcementmember has a cross-sectional centerpoint, and said reinforcement memberis positioned along said second side wall such that said centerpoint ofsaid reinforcement member is substantially-longitudinally aligned withsaid centerpoint of said third surface portion.
 13. A gas springassembly according to claim 12, wherein said flexible wall is inabutting engagement with said end wall when in saidsubstantially-longitudinally aligned position.
 14. A gas spring assemblyaccording to claim 8, wherein said second side wall includes an innersurface spaced radially-inwardly from said outer surface and extendinglongitudinally from along said end wall in approximately said seconddirection.
 15. A method of assembling a gas spring, said methodcomprising the steps of: step a) providing a flexible wall that includesan open end and an inside surface, an outside surface and an end surfaceadjacent said open end and extending between said inside surface andsaid outside surface; step b) providing a piston having a longitudinalaxis and including: an end wall disposed transverse to said axis; afirst side wall extending approximately longitudinally from said endwall in a first direction; and, a second side wall extendingapproximately longitudinally from said end wall in a second directionopposite said first direction and including a retainment ridge extendingcircumferentially around said second side wall, said retainment ridgeincluding a shoulder surface facing said end wall; said second side wallincluding an outer surface having a first surface portion disposedadjacent said end wall, a second surface portion disposed adjacent saidshoulder surface and in longitudinally-spaced relation to said firstsurface, and a third surface portion disposed between said first andsecond surface portions, said first, second and third surface portionsdefining the entirety of said outer surface between said shouldersurface and said end wall; at least one of said first and second surfaceportions defining an outermost cross-sectional dimension of said outersurface, said third surface portion at least partially defining anengagement feature along said second side wall that is positionedbetween said first and second surface portions and in spaced relation tosaid end wall and said shoulder surface of said retainment ridge; stepc) positioning said open end of said flexible wall adjacent saidretainment ridge; step d) urging said open end of said flexible wall inan axial direction toward said end wall such that said open end isforced over said retainment ridge; step e) positioning said open end ofsaid flexible wall along said second side wall such that said endsurface of said flexible wall compressively engages at least saidengagement feature of said second side wall and said outside surfaceengages said end wall.
 16. A method according to claim 15, whereinproviding a flexible wall in step a) includes providing a flexible wallthat includes a reinforcement member at least partially embedded withinsaid flexible wall adjacent said open end, and positioning said open endin step e) includes positioning said open end of said flexible wallalong said second side wall such that said reinforcement member is atleast approximately longitudinally aligned with said engagement featurealong said second side wall.
 17. A method according to claim 15, whereinproviding a piston in step b) includes providing a third surface portionhaving a concave cross-sectional shape extending radially-inwardly intosaid second side wall such that said engagement feature includes agroove extending at least partially around said outer surface.
 18. Amethod according to claim 15, wherein providing a flexible wall in stepa) includes providing a flexible wall that includes an end surface alongsaid open end having a wall surface profile, providing a piston in stepb) includes providing a piston in which said outer surface includes anouter surface profile, and positioning said open end of said flexiblewall along said second side wall in e) includes positioning said openend includes aligning said open end with said engagement feature suchthat said end surface of said flexible wall is deformed from said wallsurface profile into substantial conformity with said outer surfaceprofile.